The present invention relates to an optical system drive device for reciprocally driving an optical system of, for example, an electronic copying machine of the stationary document table type.
An electronic copying machine of the stationary document table type is known in which an optical system having an exposure lamp, mirrors or the like is reciprocally driven along a fixed document table to scan the document set thereon. A conventional optical drive device for such a copying machine uses a plurality of electromagnetic clutches which are alternately turned on and off to reciprocally drive the optical system.
FIG. 1 shows an example of a conventional optical system drive device. Referring to FIG. 1, a pair of carriage guide shafts 1 are mounted to a copying machine main body (not shown) parallel to each other. First and second carriages 3 and 5 are reciprocally movably mounted on these carriage guide shafts 1. A lamp 7 and a first mirror 9 are mounted on the first carriage 3, while a second mirror 11 is mounted on the second carriage 5. A document 13 is set on a stationary document table (not shown). Light from the lamp 7 is radiated onto the document 13, and light reflected by the document 13 becomes incident on a lens 15 through the first mirror 9 and the second mirror 11. In order to scan the document 13 by moving the first and second carriages 3 and 5 while keeping constant the length of the optical path leading from the first mirror 9 to the lens 15, an idler 17 is mounted on the second carriage 5. A wire 19 is wound around the idler 17. One end of the wire 19 is fixed and the other end thereof is fixed to and biased by, for example, a coil spring 25. The intermediate portion of the wire 19 is fixed to the first carriage 3 and is wound around a wire drum 21. The wire 19 then extends to the idler 17 again through a pulley 23 opposite the wire drum 21. The driving force of a motor 31 is transmitted to the wire drum 21 through various clutches such as a reversible clutch 27 and a speed change clutch 29. Displacement detectors or microswitches 33 are arranged along the carriage guide shafts 1 so as to detect the amount of displacement of the first and second carriages 3 and 5. The optical system of this arrangement is driven by the motor 31 and the clutches 27 and 29. When the microswitch 33 detects the displacement of the first and second carriages 3 and 5, the optical system reciprocally drives the first carriage 3 at a velocity twice that of the second carriage 5.
However, since the displacement of the first and second carriages 3 and 5 is detected by the microswitch 33, many microswitches are required in order to vary the amounts of displacement of the first and second carriages 3 and 5. This results in a complex arrangement and a low detection reliability. Furthermore, every time the clutches 27 and 29 are turned on and off, the first and second carriages 3 and 5 are subject to shock and vibration, resulting in blurring of the reproduced image. In particular, strong vibration is caused during the initialization of the first and second carriages 3 and 5. For this reason, scanning cannot be initiated until this vibration is completely damped, and the preliminary strokes of the first and second carriages 3 and 5 must be lengthened. Accordingly, the overall optical system drive device becomes large in size.